Method of washing threadlike structures



patented Apr. 8, 1941 METHOD OF WASHING THREADLIKE STRUCTURES Frank B.Ridgway, Newark, Del., assignor to E. I. du Pont de Nemours & Company,Wilmington, D'eL, a corporation of Delaware No Drawing.

Application September 25, 1937,

Serial No. 165,779

2 Claims.

This invention relates to a process of washing thread-like structures.More particularly, the invention relates to the washing of packages ofartificial threads, yarns, filaments, straw, horsehair or the like.

According to one method of producing regenerated cellulose threads bythe viscose process, the freshly coagulated, partially regeneratedthreads are wound on perforated bobbins rotating at a substantiallyconstant peripheral speed. The rayon package so produced is Washed withsoft water to free it from acids, salts and other impurities, usually bythe pressure method, for instance by mounting the perforated bobbincontaining the cake on a suitable holding device and forcing the washingliquor outwardly through the cake.

Increasing the size of the yarn packages and increasing the tensionunder which the yarn is wound on the perforated bobbins has made itextremely difficult to wash economically and without deleteriouslyaffecting the yarn. For example, when rayon is wound under a tension of0.6, 0.1 0.8 or even 1 gram per denier on to perforated bobbins in theform of cross wound packages containing 1, 2, 3, or even more pounds ofyarn, the problem becomes acute.

The desirability of producing large cakes is readily apparent sincethere are fewer units to handle in the production of a given amount ofyarn. This economy, however, is at once lost because of the prohibitiveamount of water needed to free the package from acid, salts and the likeand up to the present time no adequate solution of this problem has beenrealized.

It is therefore an object of this invention to provide an improvedprocess for economically washing packages of regenerated cellulosethreads and especially thick, dense packages of yarn wound on perforatedbobbins. Other objects will be apparent from the description thatfollows.

These objects are accomplished in general by reusing the water which hasbeen forced through the bobbin cake after the water coining through thecake has become substantially neutral. More specifically, the inventioncomprises reusing at least 50% and even as much as 80% of the waterwhich is forced through the package since it has been found that afterwashing for less than 50% and even only 10% to 20% of the total washingtime, the water coming from; the cake is substantially neutral or evenslightly alkaline, although the yarn comprising the cake is at thisperiod still decidedly acid.

Since certain portions of the cake are much tighter than other portions,especially in the case of bobbins of acid yarn wound up under hightension, the washing time must be sufficiently long to remove the lasttrace of acid from these tight portions and it requires a long time forthe water to penetrate these portions and completely remove the acid.During that part of the cycle which is necessary for removing traces ofacid from these very tight portions of the package, the amount of acidremoved, compared to the water flow, is so slight that the water doesnot become appreciably acid.

The water used may be neutral or slightly alkaline. If alkaline, thealkalinity may be due to the fact that the water used is slightlyalkaline in its natural state, or alkalinity may be induced by adding analkaline material such as NaI-ICO: or NHiOH, or both causes maycontribute to alkalinity.

The water issuing from the cake when it is first put on the wash rack isvery high in acid and salt concentrations, but these concentrations dropvery rapidly as the washing progresses. It has now been found, forinstance, that if it requires 12 hours to wash a bobbin cake of yarnacid free with a water flow through the cake of about 2 gallons perhour, the wash water coming through the cake is substantially acid freeat the end of the first hour of washing and that by the end of thesecond hour the water issuing from the cake is neutral or even slightlyalkaline (due to the natural and/or induced alkalinity of the waterused). Not only is the acid substantially all removed during the firsthour of washing, but salts and especially iron salts are also largelyeliminated during this period.

The following specific example will serve to more clearly illustratethis invention although it is to be understood that this example isgiven for illustrative purposes only and is not intended to belimitative in any way.

Example A regenerated cellulose thread of 275 denier- 120 filaments isspun under a total tension of 190 grams, and collected on a perforatedspinning bobbin 6 inches in diameter and 10 /2 inches long for such timeas to form a cake of 1.3 pounds. The yarn is laid down to form a cake ofsubstantially uniform thickness except for the beveled ends of the cake,which are of uniform slope and cover the end rows of perforations of thebobbin only sufficiently to prevent excessive flow of water under theends of the yarn package. The cake of yarn so produced is mounted on asuitable wash spindle and water admitted to the interior of theperforated bobbin under a pressure of about 45 pounds or so that about 1gallons of water pass through the cake in an hours time. During thefirst 2 hours of washing, the water passing through the cake is Wastedto the sewer or if desired, the first washings ma be conducted to arecovery system wherein the acid, salts and any other coagulating bathingredients contained in the wash water may be recovered. Thereafter thewashings are returned to the supply tank and used again. The cake wasfound to be acid free by the end of the ninth hour, but the washing wascontinued 2 hours longer as a safety precaution. The amount of wateractually consumed in washing this yarn package containing 1.3 pounds wasonly 3-gallons, or 2.3 gallons per pound of yarn. The total amount ofwater put through the cake, however, was 16.5 or nearly 13 gallons perpound of yarn. A similar test using fresh water throughout the washingcycle also consumed a total of 16.5 gallons or 13 gallons per poundsince the yarn package was freed from acid no sooner, as was determinedby pouring niethylorange on the cake from time to time during thewashing process.

By this process of recirculating and reusing the wash water, only aboutto the water consumed by the best of the prior art methods is needed towash rayon bobbin cakes free from acid and a still greater improvementis effected when compared with prior art methods using a large flow ofwater through the cakes. Rayon packages containing 1, 2 or even 3 poundsof yarn can be washed in accordance with this invention with very lowwater consumption, being no more than 7 or 8 gallons per pound of yarnand generally no more than 5 gallons per pound of yarn. As is apparent,this is a very decided saving in the cost of producing regeneratedcellulose thread.

While this invention is especially useful in connection with the washingof very large bobbins of regenerated cellulose yarn which have beenwound under relatively high tension, the invention is not so limited andmay be used with good results in the washing of smaller yarn packages,whether the yarn is wound on bobbins or other similar supports, or woundby the centrifugal bucket spinning process. Furthermore, the inventionneed not be confined to the pressure washing of yarn packages, for it isapplicable to other methods of washing, such as for instance centrifugalwashing or vacuum washing. In fact, quite probably as great savings canbe effected through the use of this process in connection with othermethods of washing as by pressure washing.

This invention has been described with reference to the washing ofregenerated cellulose thread produced by the viscose process although itis equally applicable to the washing of other threadlike structurescollected in package form, for instance regenerated cellulose threads orthe like produced by the cuprammonium cellulose process.

The water which is reused can, of course, pass through the same bobbinor other package as it initially passed through or through anotherpackage.

It is to be understood that all other variations or modifications whichconform to the spirit of the invention are intended to be includedwithin the scope of the claims.

I claim:

1. The process comprising forcing acid-free water through acid cakes ofregenerated cellulose thread, discarding the water issuing from saidacid cakes until said water issuing from said acid cakes issubstantially neutral at which point said cakes are still substantiallyacid, and thereafter reusing the water issuing from said acid cakes forfurther removal of acid from said acid cakes.

2. The process comprising forcing acid-free water through acid cakes ofregenerated cellulose thread, discarding the water issuing from saidacid cakes until said water issuing from said acid cakes issubstantially neutral at which point said cakes are still substantiallyacid, and thereafter recirculating the water issuing from said acidcakes through said acid cakes until substantially complete removal ofacid from said acid cakes is effected.

FRANK B. RIDGWAY.

